Conventionally, working vehicles such as a shovel loader and a hydraulic shovel (also called an excavator, a backhoe, etc.) have been widely known which are used to excavate ground and to move excavated earth and sand and the like. These working vehicles comprise a working device having an arm vertically swingably provided on the vehicle body configured to be movable and are configured such that various work attachments such as a bucket, a chip breaker (also simply called a breaker), and an auger device can be detachably attached to the tip of the arm. And they can efficiently perform predetermined works by replacing the attachment with another by means of detaching and attaching according to the purpose of work.
Among these working devices, there is known a device in which an attachment (e.g., a bucket) vertically swingably attached to the tip of an arm is vertically swung by a hydraulic actuator via a link mechanism (see, e.g., Japanese Laid-Open Patent Publication No. 2007-314981). As the link mechanism, there is known a mechanism configured to have a first link member pivotally joined, vertically swingably, at one end to an arm and a second link member pivotally joined, vertically swingably, at one end to an attachment and at the other end to the other end of the first link member. Further, as the hydraulic actuator, there is known an actuator configured to be pivotally joined, vertically swingably, at its base end to an arm and to be pivotally joined at its tip to the link mechanism to pivot on the pivot joint axis of the two link members.